The Collaborative International Dictionary of English v.0.48:

Bloomer \Bloom"er\, n. [From Mrs. Bloomer, an American, who
   sought to introduce this style of dress.]
   1. A costume for women, consisting of a short dress, with
      loose trousers gathered round ankles, and (commonly) a
      broad-brimmed hat.
      [1913 Webster]

   2. A woman who wears a Bloomer costume.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bloomer
    n 1: a flower that blooms in a particular way; "a night bloomer"
    2: an embarrassing mistake [syn: blunder, blooper,
       bloomer, bungle, pratfall, foul-up, fuckup, flub,
       botch, boner, boo-boo]